(1) Field of the Invention
The present invention relates to a nozzle plate as a member for forming an inkjet recording head that ejects ink droplets onto a recording medium and a method of manufacturing the same.
(2) Description of the Related Art
In an inkjet recording head that ejects ink droplets onto a recording medium to record an image, in order to improve ink ejection stability, as shown in FIGS. 10A and 10B, water repellent finishing (a water-repellent film 104) is provided on a surface of a nozzle plate 100 on which a nozzle 102 is formed. This water-repellent film 104 has the effect of stably returning ink overflowing on the nozzle surface into the nozzle (the state in FIG. 10A).
However, as shown in FIGS. 10A and 10B, in the conventional nozzle plate 100 on which the water-repellent film 104 can not be formed thicker, at the time of ink refilling after ink ejection, because the meniscus protruded from the nozzle surface due to the overshoot of meniscus expands outside the nozzle surface and extends in a lateral direction as shown in FIG. 10B, the curvature of the meniscus surface becomes larger and the surface tension of the meniscus M becomes smaller. Accordingly, the recovery time of the meniscus becomes longer, which causes a problem in the case of high-speed driving. In FIG. 10B, the recovery force of the meniscus generated by the surface tension of the meniscus is shown by the size of the arrow F2.
Further, as another problem of the water-repellent film, it is known that, when conditions (film thickness, form, or the like) of the water-repellent film are partially different on the nozzle surface, ejection directionality of the ink becomes deteriorated at the time of ink ejection. On this account, a method of uniformly and stably forming a water-repellent film on the nozzle surface (circumference of the hole) has been proposed and implemented (e.g., see JP-A-2000-280481).
However, in view of long-term reliability, because the nozzle plate surface in the inkjet recording head is a part brought into contact with an external part, there has been a problem that, at the time of maintenance of the nozzle (especially in wiping), paper jam, or the like, a scratch or chip is produced in the water-repellent film on the nozzle surface, and thereby, the defective ejection directionality of the ink is caused and predetermined image quality can not be maintained.
Further, as a measure against the problem, a form in which a counterbore larger than the nozzle diameter is provided on the nozzle surface so that a wiping blade or the like may not be in direct contact with the surface is adopted (see FIGS. 10A and 10B). However, the problem remains because the damage to the nozzle surface due to contact with the paper at the time of jam or being wiped in a state in which the paper dust is attached to the surface can not be largely improved by the method of providing a counterbore.
Further, in order to address the problem, as shown in FIG. 11, a method of entering the water repellent finishing into the nozzle interior (a water-repellent film entrance part 106) for prevention of overflow of the meniscus M and stabilization of ink ejection has been further proposed (e.g., see JP-A-2003-154663, JP-A-2001-30496, JP-A-2001-310471, and JP-A-48-37030). However, it is very difficult to control the entrance amount of the water-repellent film (=entrance amount of ink), and, if the entrance amount can not be made constant, the ejection directionality varies, which leads a large problem.
On the other hand, a technology for stabilizing the behavior of ink within the nozzle and improving ejection performance of ink by removing the water-repellent film entered into the nozzle in the process of forming the water-repellent film on the nozzle plate surface and treating nozzle interior to have a hydrophilic property (e.g., see JP-A-2001-260362). However, even in the case of this technology, there is a problem that the high-speed driving is hindered by the above described overshoot of meniscus.
Further, in the technology of JP-A-2000-280481, the water-repellent film is formed by the spin coating method or the like, and, in this case, it is necessary to suppress the upper limit of the film thickness to about 1 μm in order to obtain a well-formed uniform thin film. Therefore, it is technically difficult to form a thick water-repellent film in a good form.